In a rotary machine such as a centrifugal compressor having a rotor to which a plurality of impellers are fixed, the rotor rotates at a high speed, and thus, a desired output is generated. In the rotary machine, vibrations of the rotor during an operation thereof increase due to weight deviation or eccentricity of the rotor. In order to suppress the vibrations, a balance adjustment is performed on the rotor to which the impeller or the like is fixed so as to suppress unbalance of the rotor.
For example, PTL 1 describes a method of performing a balance adjustment in a state where a set of impellers is assembled on a rotary shaft which is a rotor of a centrifugal compressor. In this method, each time the set of impellers is attached, the balance of the rotary shaft is adjusted by cutting two different surfaces of the impeller orthogonal to the rotary shaft.
In addition, in PTL 2, by calculating and using an inclination amount of an impeller with respect to a rotary shaft, only one surface orthogonal to the rotary shaft is cut to adjust the balance of the rotary shaft. Accordingly, compared to the balance adjustment method described in PTL 1, in the balance adjustment method described in PTL 2, the number of surfaces to be processed is reduced, and thus, an operation time for the balance adjustment is shortened.
However, in a case where a plurality of impellers are attached, some impellers may become large-sized impellers with heavier weight than other impellers. In a case where some impellers are large-sized impellers, influences of the large-sized impellers on the rotor become larger than those of other impellers. That is, even when a position of the center of gravity and an inclination of the large-sized impeller are slightly changed, there is a possibility that the balance of the rotor is greatly collapsed.